1. Field of the Invention
The present invention relates to a device for controlling engine and automatic transmission of an automotive vehicle in a unified manner. More particularly, it pertains to a control device for effectively reducing the so-called "racing select shock" which occurs upon starting the vehicle in a racing state.
2. Description of the Related Art
An automatic transmission for an automotive vehicle incorporates a plurality of frictional elements including a driving clutch which is maintained disengaged in a stationary state of the vehicle (i.e. N- or P-range of the transmission) and operated into engagement upon starting the vehicle. Thus, a select operation performed from a stationary state of the vehicle into a forward or reverse running range (D- or R-range) to start the vehicle is generally accompanied by a shock which occurs along with the completion of engagement of the driving clutch. Particularly in the case of a racing selection, i.e. when a running range has been selected in a racing state in which an accelerator pedal is stepped on in the N- or P-range of the transmission, there occurs a substantial shock (racing select shock) which makes driver and/or passengers feel uncomfortable. Furthermore, when a racing selection is performed at a high engine speed, a large peak torque is generated and adversely affects various transmission components, such as propeller shaft, differential gear assembly, driving shafts, etc.
A method of alleviating racing select shock is disclosed in Japanese Patent Application Laid-open Publication No. 60-4,433, which is to perform a reduction control of a parameter representing an output power to be transmitted from an engine to driving wheels of the vehicle via an automatic transmission. More particularly, the known method is to reduce the engine output upon a racing selection, by reducing the engine speed until completion of engagement of the driving clutch, for minimizing the energy to be absorbed by the clutch. While the known method serves to more or less alleviate racing select shock, a continued reduction control after completion of engagement of the driving clutch often results in an insufficient driving torque and difficulties in starting the vehicle without engine stalling.
Moreover, the known method suffers from a problem upon racing selection during a cold start of the vehicle, in that the timing when the driving clutch is actually engaged accompanies a certain time lag due to the increased viscosity of automatic transmission fluid (ATF) and a resultant delay in the hydraulic response characteristic. At the ambient temperature of -30.degree. C., for example, it takes two to five seconds after selection of a running range until actual completion of engagement of the driving clutch. Thus, during the reduction control of the engine output, the control may become excessive and would be disadvantageous in that an excessive reduction in the engine speed often result in an undesirable tendency of engine stalling, making it practically impossible to start the vehicle.